net/http: stop ExampleServer_Shutdown from hanging on error
net/http: stop ExampleServer_Shutdown from hanging on error

Running the example code when not having permissions
to bind to port 80 will cause the program to hang after
printing the error message.

Change-Id: I2433ba2629b362fc8f1731e40cab5eea72ec354f
GitHub-Last-Rev: 0bb3dc08b6f646470fc6ff208ea12bca901a2299
GitHub-Pull-Request: golang/go#32947
Reviewed-on: https://go-review.googlesource.com/c/go/+/185157
Reviewed-by: Emmanuel Odeke <277f8eaa8c7dfbc55c17bf5e30561c1a9c45c569@gmail.com>
Run-TryBot: Emmanuel Odeke <277f8eaa8c7dfbc55c17bf5e30561c1a9c45c569@gmail.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>

akutz/go,golang/go,cloudflare/go,golang/go,cloudflare/go,cloudflare/go,cloudflare/go,cloudflare/go,golang/go,cloudflare/go,CAFxX/go,CAFxX/go,akutz/go,akutz/go,akutz/go,nawawi/go,golang/go,nawawi/go,akutz/go,akutz/go,nawawi/go,golang/go,nawawi/go,golang/go,golang/go,CAFxX/go,nawawi/go,CAFxX/go,nawawi/go,CAFxX/go,CAFxX/go,golang/go,akutz/go,cloudflare/go,akutz/go,CAFxX/go,nawawi/go,CAFxX/go,cloudflare/go,nawawi/go